When using polyurethane foams, a high degree of flame resistance is important in certain applications. This degree of flame resistance can be expressed in Standards on inflammability which can and do differ from one another depending upon the particular application envisaged, and which are often aimed at specific end uses. Standards which may be regarded in this light are the MVSS-302-Test, the Bundesbahn Test, the Lufthansa Test (FAR 25,853) and the small burner test according to DIN 53438. Much has been written on this subject of flame resistance.
Commercially, the esters of phosphorus-containing acids and derivatives thereof are used in polyurethane foams. The compounds in question include trischloroethyl phosphate (and higher homologs thereof), tricresyl phosphate, derivatives of aminomethyl phosphonic acid esters and tris-(2,3-dibromopropyl)-phosphate. Bromine-containing butene and butane diols and their relatively high molecular weight oxirane adducts, melamine and its phosphonic acid derivatives are also known flameproofing additives.
Unfortunately, the use of the above-mentioned flameproofing agents involves disadvantages for several reasons. In addition to the adverse physiological effects of .beta.-halogen esters of phosphorus, the inadequate stability to hydrolysis of compounds of this class is a serious disadvantage. This is particularly unpleasant to the compounder of the polyurethane starting components, because the addition reaction is of course known to be catalyzed by compounds containing tertiary amino groups. Due to this instability of the flameproofing agents used (which is even worse in the basic range) formulations of the starting materials show only limited storage stability. Changes in activity lasting several hours are even observed in formulations freshly prepared just before processing. In general, they can only be corrected with considerable difficulty, the parts affected being regarded as waste because post-catalysis involves many problems.
Additionally, conventional flameproofing agents also have a plasticizer effect which is reflected in a considerable reduction in the thermal stability of the foam under load. In addition, conventional flameproofing agents undergo a gradual loss of activity through the volatility of the compounds used. In automobiles, for example, this diffusability is reflected in the form of recurring deposits on glass surfaces such as windshields (fogging).
The object of the present invention is to provide reactive flameproofing compounds for polyurethane foams which do not have any of the disadvantages of the prior art, namely
inadequate dispersibility or miscibility;
inadequate stability in storage of the mixture of starting materials containing flameproofing agents;
plasticizing effects of the flameproofing agent;
poor thermal stability of the foam under load caused by the additives;
diffusion effects and exudation of the flameproofing agent, i.e. a reduction in activity; and
emission of hydrohalides in the event of fire.